Evapotranspiration measurements in the north China plain: insights from multi-years of lysimeter and eddy covariance system

Precise estimates of actual evapotranspiration (ET_a) are crucial for enhancing our understanding of the water and energy exchanges between land and atmosphere. These estimates are essential for applications and advancements in meteorological, climatological, ecological, and hydrological research. This study compares ET measurements obtained by two commonly used methods: eddy covariance (EC) and lysimeter (LY), based on long-term parallel measurements from 2012 to 2020. The analyses reveal a pronounced seasonal cycle in all measurements, with the highest values observed in summer and the lowest in winter. ET measurements from two lysimeters showed a significant difference of about 30% between areas of vegetation and bare soil. The ET values from the lysimeter method showed good agreement with the EC measurements, with an approximate difference of 7% between the two methods. Additionally, precipitation estimates from the lysimeter method were slightly higher than those from rain gauge measurements. The study identified air temperature as the primary controlling factor of ET, contributing nearly 60%. Net radiation and NDVI also played significant roles, with contributions larger than 10% and approximately 10%, respectively. The main causes of discrepancies between lysimeter and EC measurements were attributed to different measurement scales, varying crop growth stages, and soil moisture conditions. This study quantified ET at two different scales in nine-year period, providing valuable insights into the rational utilization of water resources in the region. The findings underscore the importance of considering measurement scales and environmental conditions when interpreting ET data for water resource management.